Methods of forming dielectric layers and methods of forming capacitors

ABSTRACT

Methods of forming dielectric layers and methods of forming capacitors are described. In one embodiment, a substrate is placed within a chemical vapor deposition reactor. In the presence of activated fluorine, a dielectric layer is chemical vapor deposited over the substrate and comprises fluorine from the activated fluorine. In another embodiment, a fluorine-comprising material is formed over at least a portion of an internal surface of the reactor. Subsequently, a dielectric layer is chemical vapor deposited over the substrate. During deposition, at least some of the fluorine-comprising material is dislodged from the surface portion and incorporated in the dielectric layer. In another embodiment, the internal surface of the reactor is treated with a gas plasma generated from a source gas comprising fluorine, sufficient to leave some residual fluorine thereover. Subsequently, a substrate is exposed within the reactor to chemical vapor deposition conditions which are effective to form a dielectric layer thereover comprising fluorine from the residual fluorine.

TECHNICAL FIELD

[0001] This invention relates to methods of forming dielectric layersand to methods of forming capacitors.

BACKGROUND OF THE INVENTION

[0002] Dielectric material layers are essential components in integratedcircuitry capacitors, and are typically interposed between two capacitorplates. Capacitors are used in memory circuits, such as dynamic randomaccess memory (DRAM) arrays.

[0003] As device dimensions continue to shrink, an important emphasis isplaced on maintaining, and in some instances, increasing a capacitor'sability to store a desirable charge. For example, a capacitor's chargestorage capability can be increased by making the capacitor dielectricthinner, by using an insulator with a larger dielectric constant, or byincreasing the area of the capacitor. Increasing the area of a capacitoris undesirable because the industry emphasis is on reducing overalldevice dimensions. On the other hand, providing a thinner capacitordielectric layer and/or using an insulator with a larger dielectricconstant can present problems associated with current leakage, such asthat which can be caused by Fowler-Nordheim Tunneling. Current leakagecan significantly adversely impact the ability of a capacitor to store acharge.

[0004] This invention grew out of needs associated with providingmethods of forming dielectric layers having sufficiently high dielectricconstants. This invention also grew out of needs associated withproviding methods of forming capacitor constructions which have sdesirable charge storage characteristics, and reduced current leakage.

SUMMARY OF THE INVENTION

[0005] Methods of forming dielectric layers and methods of formingcapacitors are described. In one embodiment, a substrate is placedwithin a chemical vapor deposition reactor. In the presence of activatedfluorine, a dielectric layer is chemical vapor deposited over thesubstrate and comprises fluorine from the activated fluorine. In anotherembodiment, a fluorine-comprising material is formed over at least aportion of an internal surface of the reactor. Subsequently, adielectric layer is chemical vapor deposited over the substrate. Duringdeposition, at least some of the fluorine-comprising material isdislodged from the surface portion and incorporated in the dielectriclayer. In another embodiment, the internal surface of the reactor istreated with a gas plasma generated from a source gas comprisingfluorine, sufficient to leave some residual fluorine thereover.Subsequently, a substrate is exposed within the reactor to chemicalvapor deposition conditions which are effective to form a dielectriclayer thereover comprising fluorine from the residual fluorine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0007]FIG. 1 is a schematic diagram of a chemical vapor depositionreactor in accordance with one aspect of the invention.

[0008]FIG. 2 is a view of a portion of the reactor.

[0009]FIG. 3 is a view of a portion of the reactor.

[0010]FIG. 4 is a schematic diagram of another reactor in accordancewith another aspect of the invention.

[0011]FIG. 5 is a view of the FIG. 1 reactor at a processing step inaccordance with one aspect of the invention.

[0012]FIG. 6 is a diagrammatic side sectional view of a portion of awafer fragment, in process, in accordance with one aspect of theinvention.

[0013]FIG. 7 is a view of the FIG. 6 wafer fragment at a differentprocessing step.

[0014]FIG. 8 is a graph of capacitance versus leakage current.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful artsy” (Article 1, Section 8).

[0016] Referring to FIG. 1, a chemical vapor deposition reactor is showngenerally at 10. Reactor 10 can comprise any suitable reactor which iscapable of processing substrates as described below. The illustratedreactor includes a pair of electrodes 12, 14 which can be biased by anRF source 16. RF source 16 can be used, in one implementation, togenerate a gas plasma within the reactor. Various other reactor typesand designs, some of which can be used in connection with variousaspects of the invention, are described in a text by Lieberman andLichtenberg, entitled Principles of Plasma Discharges and MaterialsProcessing, the disclosure of which is incorporated by reference.

[0017] Reactor 10 is typically used to chemical vapor deposit variouslayers over a substrate (not shown) and can include a source 18 throughwhich various precursor gases are provided and processed. Such gases canalso be provided through an electrode, such as electrode 12.

[0018] Referring to FIGS. 1-3, reactor 10 includes an internal surface20 which defines a processing chamber in which processing takes place.The illustrated reactor is depicted at a processing point prior toplacement of a substrate therein. A halogen-comprising material,preferably a fluorine-comprising material 22 (FIG. 2), 24 (FIG. 3), isformed over at least a portion of surface 20. In a most preferredaspect, halogen-comprising material comprises activated fluorine. By“activated” is meant that the material can include ions, radicals,electrons, and other excited species having lifetimes which areinfluenced by various factors.

[0019] One way of providing the activated fluorine material 22, 24 is togenerate a fluorine-comprising gas plasma having activated fluorinetherein. Such plasma can be generated by introducing afluorine-comprising source gas, such as NF₃, into the reactor, andsubjecting the source gas to processing conditions which are effectiveto form the gas plasma. Such processing conditions can include, in thereactor illustrated in FIG. 1, subjecting the source gas to suitable RFenergy sufficient to form the plasma. Accordingly, internal surface 20is treated with the gas plasma prior to introduction of a substratetherein. Such treatment effectively leaves residual activated fluorineover surface 20 in the absence of a substrate. Accordingly in thisexample, the substrate is not exposed to the gas plasma. Coverage ofsurface 20 by the activated fluorine can be non-uniform, as shown inFIG. 3. Preferably, at least some of the residual activated fluorine ispresent during the chemical vapor depositing of a dielectric layer whichis described just below.

[0020] In this example, and because the substrate is not present in thereactor during formation of the gas plasma, the gas plasma is formedaway from the substrate. Accordingly, the reactor is preferablysubstantially, if not completely, plasma-free during the depositing ofthe dielectric layer. By “substantially” is meant that it can bepossible, in some reactor types, for plasma to exist in the reactorsubstantially remote of the substrate. Such is more likely to occur withthe reactor design illustrated in FIG. 4. There, a reactor 26 includes aremote plasma source 28 operably coupled therewith. Source 28 ispreferably one which is capable of generating a gas plasma, from thefluorine-comprising source gas, which is subsequently flowed intoreactor 26. In this way, a gas plasma is formed away from any substratewhich might be present in FIG. 4. Remote plasma processing andapparatuses for conducting such processing are described in U.S. Pat.No. 5,180,435, entitled “Remote Plasma Enhanced CVD Method and Apparatusfor Growing an Epitaxial Semiconductor Layer”, the disclosure of whichis incorporated by reference. In the illustrated example, onlyelectrodes 12 a, 14 a are shown. A substrate is not specificallydepicted in the FIG. 4 example. A substrate could, however, be presentin reactor 26 during formation of, and subsequent flowing of theactivated fluorine from remote plasma source 28.

[0021] Referring to FIG. 5, a substrate 30 is placed within reactor 10,and preferably after the internal walls of the reactor have beenpre-treated with the fluorine-comprising gas plasma. In the presence ofactivated fluorine within the reactor, the substrate is exposed toconditions which are effective to chemical vapor deposit a dielectriclayer over the substrate which comprises fluorine from the activatedfluorine. Processing conditions under which dielectric layers can bedeposited include using liquid chemical precursors including tantalumpentaethoxide (TAETO) or tantalum tetraethoxide dimethylaminoethoxide(TAT-DMAE), at temperatures from between about 400° C. to 500° C., andpressures from between about 30 mTorr to 30 Torr. Other precursors suchas BST precursors, e.g. M(thd)₂, where M is either Ba or Sr, attemperatures from between about 500° C. to 650° C., and pressures frombetween about 30 mTorr to 30 Torr, can be used.

[0022] Preferably, the dielectric layer has a dielectric constant or “k”value which is greater than about 6. Exemplary materials for thedielectric layer can include silicon nitride (“k” value of around 7),tantalum pentoxide (Ta₂O₅)(“k” values ranging from about 10-25), BST(“k” values ranging from about 100 to 1000 or greater). The dielectriclayer preferably comprises less than about 10% fluorine, by weight. Morepreferably, the dielectric layer comprises between about 0.001% and 10%fluorine, by weight.

[0023] Referring to FIGS. 6 and 7, a capacitor forming method isdescribed relative to a substrate 32. Such can comprise any suitablesubstrate over which a capacitor is to be formed. An exemplary capacitorformed in connection with dynamic random access memory circuitryincludes a substrate comprising insulative materials, such asborophosphosilicate glass. A first capacitor plate 34 is formed oversubstrate 32, typically, by chemical vapor deposition of polysilicon. Inthe presence of activated fluorine, as described above, a dielectriclayer 36 is chemical vapor deposited over first capacitor plate layer34. A second capacitor plate layer 38 is formed over dielectric layer 36to provide a capacitor construction.

[0024] In one reduction-to-practice example, an Applied Materials 5000processing chamber was cleaned, prior to introduction of a substratetherein, with a remote NF₃ plasma under the following processingconditions: 1500 sccm of NF₃, 1800-3200 watts at around 2 Torr for aduration of about 100 seconds. After the plasma clean, a semiconductorwafer was placed in the chamber and a dielectric layer, such as thoselayers described above, was formed over the wafer. The followingconditions were used: temperature of around 475° C. with 300 sccmTAT-DMAE, 250 sccm of O₂, spacing of 350 mils, and a pressure of 1 Torr.

[0025]FIG. 8 illustrates, for the reduction-to-practice example, a graphof capacitance versus leakage current for two areas over the wafer. Datapoints, collectively grouped at 40, correspond to capacitance andleakage current measurements taken at or near the center of the wafer.Data points, collectively grouped at 42, correspond to capacitance andleakage current measurements taken at or near the edge of the wafer. Asa consequence of the chamber geometry of the Applied Materials 5000chamber, more residual fluorine-comprising material (e.g. activatedfluorine), is prevalent at the edge of the wafer. Hence, the edge of thewafer is more influenced by the above-described treatment than otherwafer portions such as those at or near the center of the wafer.Plotting capacitance versus leakage for the two areas indicates that thecapacitance achieved at or near the edge of the wafer (i.e.,corresponding to data points 42) is generally greater than thecapacitance at or near the center of the wafer (i.e., corresponding todata points 40). In addition, data points 42 constitute wafer areasgenerally having less leakage current for a given capacitance than thosedefined by data points 40. Accordingly, for some of the data points, anoverall increase in capacitance was observed with a lowering of theleakage current. In addition, the deposition rate of the dielectriclayer was observed to increase in the presence of the residual activatedfluorine.

[0026] Accordingly, the methods described above permit dielectric layershaving increased dielectric constants to be formed. Such permitscapacitors having reduced dimensions to be formed with desirable chargestorage characteristics.

[0027] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a dielectric layer comprising: placing asubstrate within a chemical vapor deposition reactor; and in thepresence of activated fluorine within the reactor, chemical vapordepositing a dielectric layer over the substrate comprising fluorinefrom the activated fluorine.
 2. The method of claim 1 further comprisingproviding activated fluorine over an interior surface of the reactorprior to chemical vapor depositing the dielectric layer.
 3. The methodof claim 1 further comprising providing activated fluorine over aninterior surface of the reactor prior to placing the substrate withinthe chemical vapor deposition reactor.
 4. The method of claim 3, whereinthe providing of the activated fluorine over the interior surface of thereactor comprises providing the activated fluorine from a gas plasma. 5.The method of claim 1 further comprising generating a gas plasmacomprising the activated fluorine, the substrate not being exposed tothe gas plasma.
 6. The method of claim 1 further comprising generating agas plasma comprising the activated fluorine, the gas plasma beingremote from the reactor.
 7. The method of claim 1, wherein thedielectric layer has a “k” value greater than about six.
 8. A method offorming a dielectric layer comprising: providing a chemical vapordeposition reactor having an internal surface; forming afluorine-comprising material over at least a portion of the reactorinternal surface; and after said forming, chemical vapor depositing adielectric layer over a substrate within the reactor and dislodging atleast some of the fluorine-comprising material from the surface portionto incorporate at least some fluorine of the fluorine-comprisingmaterial in the dielectric layer.
 9. The method of claim 8, wherein theforming of the fluorine-comprising material comprises forming activatedfluorine over the surface portion.
 10. The method of claim 8, whereinthe forming of the fluorine-comprising material comprises generating afluorine-comprising gas plasma having activated fluorine therein whichis formed over the surface portion.
 11. The method of claim 8, whereinthe forming of the fluorine-comprising material comprises generating afluorine-comprising gas plasma remote from the chemical vapor depositionreactor, the gas plasma having activated fluorine therein, and providingat least some of the activated fluorine from the gas plasma over thesurface portion.
 12. The method of claim 8, wherein the forming of thefluorine-comprising material comprises generating a gas plasma from asource gas comprising NF₃, the plasma having activated fluorine thereinwhich is formed over the surface portion.
 13. The method of claim 8,wherein the forming of the fluorine-comprising material comprisesgenerating a gas plasma from a source gas consisting of NF₃, the plasmahaving activated fluorine therein which is formed over the surfaceportion.
 14. The method of claim 8, wherein the forming of thefluorine-comprising material comprises generating a gas plasma from asource gas comprising NF₃, the plasma being remote from the chemicalvapor deposition reactor, the gas plasma having activated fluorinetherein, and providing at least some of the activated fluorine from thegas plasma over the surface portion.
 15. The method of claim 8, whereinthe dielectric layer comprises tantalum pentoxide.
 16. A method offorming a dielectric layer comprising: providing a chemical vapordeposition reactor having an internal surface; treating the internalsurface with a gas plasma generated from a source gas comprising NF₃sufficient to leave some residual fluorine thereover; and after saidtreating, exposing a substrate within the reactor to chemical vapordepositing conditions effective to form a dielectric layer thereovercomprising fluorine from the residual fluorine.
 17. The method of claim16, wherein at least some of the residual fluorine comprises activatedfluorine.
 18. The method of claim 16, wherein at least some of theresidual fluorine comprises activated fluorine which is present duringthe chemical vapor depositing of the dielectric layer.
 19. The method ofclaim 16, wherein the exposing of the substrate to chemical vapordepositing conditions comprises doing so in the absence of the gasplasma.
 20. The method of claim 16, wherein the dielectric layercomprises a material having a “k” value greater than about six.
 21. Themethod of claim 16, wherein the dielectric layer comprises tantalumpentoxide.
 22. The method of claim 16, wherein the dielectric layercomprises less than about 10% by weight of fluorine.
 23. The method ofclaim 16, wherein the dielectric layer comprises between about 0.001%and 10% by weight of fluorine.
 24. A method of forming a capacitorcomprising: placing a substrate within a chemical vapor depositionreactor; forming a first capacitor plate layer over the substrate;providing activated fluorine within the reactor; and in the presence ofactivated fluorine within the reactor, chemical vapor depositing adielectric layer over the first capacitor plate layer comprising atleast some fluorine from the activated fluorine over the substrate; andforming a second capacitor plate layer over the dielectric layer. 25.The method of claim 24, wherein the providing of the activated fluorinecomprises forming a gas plasma from a fluorine-comprising source, theplasma having at least some activated fluorine therein which is providedwithin the reactor.
 26. The method of claim 25, wherein the gas plasmais formed away from the substrate.
 27. The method of claim 24, whereinthe providing of the activated fluorine comprises: providing a remoteplasma source operably coupled with the reactor; in the remote plasmasource, generating a gas plasma from a fluorine-comprising source gas,the plasma including activated fluorine; and flowing activated fluorinefrom the gas plasma into the reactor.
 28. The method of claim 27,wherein the substrate is not exposed to the gas plasma.
 29. The methodof claim 27, wherein the reactor is substantially plasma-free during thedepositing of the dielectric layer.
 30. The method of claim 27, whereinthe reactor is plasma-free during the depositing of the dielectriclayer.
 31. The method of claim 27, wherein the fluorine-comprisingsource gas comprises NF₃.
 32. The method of claim 24, wherein thedielectric layer comprises material having a “k” value greater thanabout six.
 33. A method of forming a dielectric layer comprising:placing a substrate within a chemical vapor deposition reactor; and inthe presence of activated halogen species within the reactor, chemicalvapor depositing a dielectric layer over the substrate comprisingmaterial from the activated halogen species.
 34. The method of claim 33further comprising providing activated halogen species over an interiorsurface of the reactor prior to chemical vapor depositing the dielectriclayer.
 35. The method of claim 33 further comprising providing activatedhalogen species over an interior surface of the reactor prior to placingthe substrate within the chemical vapor deposition reactor.